package com.finch.juc;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * @author Levi Wang
 * @create 2021-07-21 22:40
 *
 * 多个线程同事读一个资源类没有任何问题，所以为了满足并发量，读取共享资源应该可同时进行
 * 但是，如果有一个线程想去写共享资源了，就不应该再有其他线程可以对资源进行读或写
 * 即
 * 读读能共存
 * 读写不能共存
 * 谢谢不能共存
 *
 */

//错误示范
class MyCache1 {
    private volatile Map<String, Object> map = new HashMap<>();

    public void put(String key, Object value){
        System.out.println(Thread.currentThread().getName()+"\t ----开始写入");
        try {
            TimeUnit.MILLISECONDS.sleep(300);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        map.put(key,value);
        System.out.println(Thread.currentThread().getName()+"\t ----写入完成");
    }

    public void get(String key){
        System.out.println(Thread.currentThread().getName()+"\t 开始读取");
        try {
            TimeUnit.MILLISECONDS.sleep(300);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        Object result = map.get(key);
        System.out.println(Thread.currentThread().getName()+"\t 读取完成");
    }

}


//正确写法
class MyCache {
    private volatile Map<String, Object> map = new HashMap<>();
    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    public void put(String key, Object value){

        readWriteLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"\t ----开始写入");
            try {
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            map.put(key,value);
            System.out.println(Thread.currentThread().getName()+"\t ----写入完成");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            readWriteLock.writeLock().unlock();
        }
    }

    public void get(String key){
        readWriteLock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"\t 开始读取");
            try {
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            Object result = map.get(key);
            System.out.println(Thread.currentThread().getName()+"\t 读取完成");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            readWriteLock.readLock().unlock();
        }
    }

}




public class ReadWriteLockDm {

    public static void main(String[] args) {

//        MyCache1 myCache = new MyCache1();

        MyCache myCache = new MyCache();

        for (int i = 1; i <= 5; i++) {
            final int tmpInt = i;
            new Thread( () -> {
                myCache.put(tmpInt + "", tmpInt + "");
            }, String.valueOf(tmpInt)).start();
        }

        for (int i = 1; i <= 5; i++) {
            final int tmpInt = i;
            new Thread( () -> {
                myCache.get(tmpInt + "");
            }, String.valueOf(tmpInt)).start();
        }


    }

}

















